1. Field of the Invention
The present invention relates to portable abrasive grinders in which particles abraded from a work surface are withdrawn by suction through a tool shroud to a collection location.
2. Description of the Prior Art
Abrasive grinders of the type under consideration are of a known general type comprising a portable body which is adapted to be held by a user and which contains a motor acting to drive a backing plate which in turn carries an abrasive disk for abrading a work surface. In the "vacuum" type grinder, a shroud in the vicinity of the backing plate and abrasive disk defines a chamber through which air and entrained particles flow to an outlet leading to an accumulation point. The abrasive disk and backing plate are provided with holes which, when aligned, form an air passage to allow the flow of air and entrained particles which were drawn by suction to the shroud.
For economy in employing such abrasive disks in fabrication operations, it is essential that the labor cost be minimized by making the abrasive disk easily replaceable on the backing plate in a rapid and convenient manner. Many of the commercially available disks are provided with an adhesive backing which is peeled off during installation. The disk holes and backing plate holes are manually aligned. This process is time consuming and can result in misalignment of the disk and backing plate holes. Although quick attach couplings have been provided for abrasive disks in such patents as U.S. Pat. No. 26,552, Re. to Block, issued Mar. 25, 1969, such prior devices have not provided a method for aligning the disk holes with the corresponding holes provided in the backing plate of a vacuum type abrasive grinder.
Another problem in the prior art devices is the tendency for the rapid rotary motion of the grinder backing plate to cause abraded particles contacting the unit to move radially outward under the influence of centrifugal force, with the tendency for some particles to escape the periphery of the backing plate and shroud. One attempt to overcome this problem has been the provision of a resilient lip seal carried by the shroud for contacting an upper surface of the backing plate during use. See, for example, U.S. Pat. No. 4,531,329 to Huber, issued Jul. 30, 1985. However, contact between the seal and backing plate can retard or even arrest movement of the sanding member or movement of the machine over the work area. I have surprisingly discovered that the provision of a controlled gap between the backing plate and shroud produces improved results with high speed grinders operating in the 12,000-24,000 r.p.m. range.
The present invention has as its object an improved dust control system which features the synergistic effect of a controlled gap between the shroud and upper surface of the backing plate along with flow passages formed by the aligned holes provided in the backing plate and abrasive disk.
The present invention also has as its object an improved quick attach method for attaching an abrasive disk to the backing plate which automatically aligns the corresponding holes in the disk and backing plate which are used as flow passages for the air and entrained particles which flow from the work surface to the shroud.
Additional objects, features and advantages will be apparent in the written description which follows.